Power control method and user equipment in device to device communication in serving cell

ABSTRACT

The present disclosure provides a power control method in device to device (D2D) communication and a user equipment for performing the power control method. The method includes computing a power value of device to device (D2D) transmission of a user equipment performing D2D communication in a subframe in a serving cell, based on a power control adjustment state of a Long Term Evolution (LTE) wide area network (WAN) uplink channel of the user equipment and an offset or a ratio indicated by a transmit power control (TPC) command indicated in D2D grant or downlink control information (DCI) format 3/3A.

BACKGROUND Technical Field

The present disclosure relates to the field of wireless communication,and particularly, to a power control method and user equipment in deviceto device (D2D) communication in a serving cell.

Description of the Related Art

The D2D communication is direct communication between devices, and suchkind of communication could happen within network coverage and withoutnetwork coverage.

FIG. 1 shows a situation in which D2D direct communication is performedwithin network coverage and D2D direct communication is performedwithout network coverage.

As shown in FIG. 1 , user equipments 101 and 102 directly communicatewithin network coverage of an E-UTRAN node B (eNB) 100, while userequipments 103 and 104 directly communicate without network coverage ofthe eNB 100.

When D2D user equipments are in a Long Term Evolution (LTE) wide areanetwork (WAN), they may be operated in LTE WAN and D2D communicationsimultaneously. That means, in some radio resources/subframes, D2D userequipments transmit/receive LTE WAN signals, but in other radioresources/subframes, D2D user equipments transmit/receive D2D signals.This also depends on which mode D2D user equipments are operated in.Currently there are two modes that a user equipment could be operatedin: mode 1 in which an eNB (like base station) or a release-10 relaynode schedules exact resources used by a user equipment to transmitdirect data and direct control information; and mode 2 in which a userequipment on its own selects resources from resource pools to transmitdirect data and direct control information.

In mode 1, the resources for D2D transmission are allocated or fullycontrolled by the eNB, but in mode 2, the user equipment itself selectsthe resources for D2D transmission. Generally, in mode 1, D2D userequipments (for example in RRC_CONNECTED) could receive dedicated RRCsignaling from the eNB, but in mode 2, D2D user equipments (for examplein RRC_IDLE) can only receive common RRC signaling, for example, asystem information block (SIB). In this document, the focus is mainlyuser equipments in mode 1.

If D2D resources and LTE WAN resources are multiplexed in the samesubframe, there are problems of in-band emission and inter-carrierinterference. The first problem means that a D2D signal may cause powerleakage to neighbor LTE WAN signals in the frequency domain in the samesubframe. The second problem somehow has a meaning similar to the firstproblem but it may be caused by other reasons, for example, whether thetiming of signals are aligned. If a D2D signal uses an extended cyclicprefix (CP) but an LTE WAN signal uses a normal CP (NCP), which meansthe timing of two types of signals are not aligned, it may lead tointer-carrier interference.

SUMMARY

The present disclosure is made in view of the above consideration.

In one general aspect, the techniques disclosed here feature a powercontrol method including computing a power value of device to device(D2D) transmission of a user equipment performing D2D communication in asubframe in a serving cell, based on a power control adjustment state ofa Long Term Evolution (LTE) wide area network (WAN) uplink channel ofthe user equipment and an offset or a ratio indicated by a transmitpower control (TPC) command indicated in D2D grant or downlink controlinformation (DCI) format 3/3A.

In another aspect, there is provided a computer program product. Thecomputer program product includes a storage medium which may be accessedby a computer and store instructions which are executed by the computerto perform each step of the power control method provided by the aboveaspect.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a situation in which D2D direct communication is performedwithin network coverage and D2D direct communication is performedwithout network coverage;

FIG. 2 shows a flowchart of a power control method according to anembodiment of the present disclosure;

FIG. 3 shows an example of subframes of a user equipment according to anembodiment of the present disclosure;

FIG. 4 shows an example of multiple D2D groups in the same serving cellaccording to an embodiment of the present disclosure; and

FIG. 5 shows a block diagram of the user equipment according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part thereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. It will be readily understood that the aspects ofthe present disclosure can be arranged, substituted, combined, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated and make part of this disclosure.

Power control was approved already by many companies in the 3rdGeneration Partnership Project (3GPP) as a good/valid solution to solveabove two problems compared with other solutions. For example, the othersolutions may be as follows. A guard band is used to solve the in-bandemission issue, but resources are wasted; aligned timing (the same CP ortiming advance) between a D2D communication and an LTE WAN communicationis used, but the issue is that it may not solve the in-band emission. OrLTE WAN resources are not allocated in D2D subframes to avoid the aboveproblems, but it may give a big impact to WAN physical uplink controlchannel (PUCCH) timing specification or LTE WAN resource utilization. Sofrom this point of view, the power control is a very promising/necessarysolution in the D2D transmission. But of course, the power control couldalso combine any of the above three solutions.

On the other hand, however, the problem about the D2D power control isthat many details are not concluded yet, for example, the followingissues: how to control the D2D power to reduce interference to LTE WANresources, how to accumulate power for D2D and LTE WANsignals/subframes, how to configure power control parameters fordifferent D2D user equipments, and what the TPC command range is.

One straightforward solution is that the D2D and LTE WANsignals/subframes adopt totally independent power control mechanisms(including open-loop components like P₀ and alpha (a) and closed-loopcomponents like fc( )). The merit of such solution is that the eNB couldadjust D2D power flexibly without caring about LTE WAN interference, andit is friendly to the D2D coverage. But the problems of this solutionare: (1) the eNB can not accurately control D2D power to reduceinterference to the LTE WAN due to inaccurate knowledge of LTE WANtransmission power (the eNB does not know fc( )) and D2D transmissionpower (no D2D power headroom report (PHR) and reference signal receivedpower (RSRP) so far); and (2) the user equipment complexity is increaseddue to dual independent power accumulation functions.

Another straightforward solution is that open-loop power controlparameters like P₀ and alpha of D2D communication are independentlyconfigured between D2D and LTE WAN signals/subframes, but anaccumulation function is shared between D2D and LTE WANsignals/subframes. That means that subframe i's power (LTE WAN subframe)will be accumulated to subframe i+1's power (D2D subframe) for the sameuser equipment or vice versa. The merit of such solution is that it onlyconsiders one accumulation function. But the problems of this solutionare: (1) LTE WAN power/performance is impacted by D2D power (mutualimpact); and (2) it may lead to very dynamic WAN signal power change ineNB reception, and instable receiving performance results in thatautomatic gain control (AGC) in radio frequency (RF) part can not workwell.

FIG. 2 shows a flowchart of a power control method according to anembodiment of the present disclosure.

As shown in FIG. 2 , the power control method according to theembodiment includes step S201. In step S201, a power value of device todevice (D2D) transmission of a user equipment performing D2Dcommunication in a subframe in a serving cell is computed based on apower control adjustment state of an LTE wide area network (WAN) uplinkchannel of the user equipment and an offset or a ratio indicated by aTPC command indicated in D2D grant or DCI format 3/3A.

According to an embodiment of the present disclosure, in the above powercontrol method, the uplink channel is any of a PUSCH, an SRS, and aPUCCH or a combination of them.

According to an embodiment of the present disclosure, in the above powercontrol method, the power value is further decided by open-loopparameters including P₀ and alpha (α) of D2D communication configured bymedia access control (MAC) layer signaling or radio resource control(RRC) signaling.

Specifically, if the uplink channel is a PUSCH, the power value may becalculated by the following formula (1).

10 log₁₀(M _(D2D,c)(i))+P _(D2D,c)(j)+α_(D2D,c)(j)·PL _(c)+Δ_(TF,c)(i)+f_(c)(i−1)+δ_(D2D,c)(i−K _(D2D))  (1)

Here, the parameter M_(D2D,c) (i) is the bandwidth of the D2D resourceassignment expressed in number of resource blocks valid for the subframei and the serving cell “c”. The parameter P_(D2D,c)(j) is a parameterwhich means a targeted received power of an eNB of the serving cell “c”.The parameter “j” means different grant types, for example, in PUSCHtransmissions, in case of a semi-persistent grant, then j=0, in case ofa dynamic scheduled grant, then j=1, and in case of a random accessresponse grant, then j=2. According to another embodiment, the parameterP_(D2D,c)( ) may also be fixed in specification instead of multiplevalues.

The parameter PL_(c) is the downlink pathloss estimate (between the eNBand D2D user equipment) calculated in the user equipment for the servingcell “c” in dB, and PL_(c)=referenceSignalPower−higher layer filteredRSRP. Here, “referenceSignalPower” may be provided by high-layersignaling. The parameter α_(D2D,c)(j) is a compensation coefficient ofthe downlink pathloss PL_(c). According to another embodiment of thepresent disclosure, in the above power control method, for j=0 or 1,α_(c)(j)∈{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} is a 3-bit parameterprovided by higher layer signaling for the serving cell “c”, and forj=2, α_(c)(j)=1.

The parameter Δ_(TF,c) (i) is a minor offset similar to that of thecurrent PUSCH power control formula.

The power control adjustment state of LTE WAN uplink channel of the userequipment in the latest LTE WAN subframe is f_(c)(i−1). That could beaccumulated/absolute power value of an uplink subframe immediatelybefore the subframe i, of the same user equipment in the LTE WAN. Andsuch value is adjusted by a TPC command indicated by LTE WAN subframegrant, for example, DCI format 0/4 or DCI format 3/3A, used for PUSCHpower adjustment.

In the present embodiment, the offset or ratio indicated by the TPCcommand may be the parameter δ_(D2D,c) (i−K_(D2D)), which is acorrection value used for the D2D communication, and included in the D2Dgrant or indicated in DCI format 3/3A, in which there are two options:option (1), the D2D TPC command and the LTE WAN TPC command are locatedin the same DCI format 3/3A; and option (2), only the D2D TPC commandsare in DCI format 3/3A.

In the present embodiment, the offset and/or ratio indicate only zero ora negative value. For example, if δ_(D2D,c)(i−K_(D2D)) indicates theoffset, the value range of δ_(D2D,c)(i−KD2D) is {0, −10}dB, and ifδ_(D2D,c)(i−K_(D2D)) indicates the ratio, the value range ofδ_(D2D)(i−K_(D2D)) is 10, −0.11 dB. In this case, the length of suchfield is 1 bit. In case the length of such field is 2 bits, the rangecould be further extended, for example {0, −5, −10, −15}dB.

Further, when δ_(D2D,c)(i−K_(D2D)) indicates the ratio, the formula (2)is used for computing the power control value of the user equipment inD2D communication.

10 log₁₀(M _(D2D,c)(i))+P _(D2D,c)(j)+α_(D2D,c)(j)·PL _(c)+Δ_(TF,c)(i)+f_(c)(i−1)+δ_(D2D,c)(i−K _(D2D))f _(c)(i−1)   (2)

Compared with the formula (1) in the above embodiment, the onlydifference of the formula (2) is that a ratio to PUSCHaccumulation/absolute power “f_(c)(i−1)” is used. And such ratio is alsoindicated in the D2D grant or DCI format 3/3A. Here, since the TPCcommand range for such ratio could be, for example, {0, −0.1}dB, onlyreduction to the PUSCH power is considered here for the D2D power.

FIG. 3 shows an example of subframes of the same user equipment used forD2D and LTE WAN communication according to an embodiment of the presentdisclosure.

As shown in FIG. 3 , there are illustrated five subframes in the timedomain direction used for the same user equipment, that is, subframe 1,subframe 2, subframe 3, subframe 4, and subframe 5, and assuming thatsubframes 2 and 5 are used for the D2D communication of the userequipment, and subframes 1, 3 and 4 are used for the LTE WANcommunication of the same user equipment. For example, it is hereassumed that “i”=5, that is, the user equipment needs to calculate theD2D power control for subframe 5, so the user equipment will copy theadjustment state “f_(c)(i−1)” of the PUSCH channel in the WAN subframe 4for the D2D subframe 5, and add the parameter (δ_(D2D,c)(i−K_(D2D)))indicated in the subframe 1 by the eNB for the final adjustment state ofD2D communication based on the formula (1). Here, the K_(D2D) is 4. Theopen-loop parameters like P_(D2D,c)(j) and α_(D2D,c)(j) are indicatedvia an SIB.

From this example, it can be seen that the D2D user equipment does notneed accumulation power specially for D2D subframes. Instead, it justcopies f_(c)(i−1) of the PUSCH and adds a dynamic adjustment value(δ_(D2D,c) (i−K_(D2D))) indicated in the TPC command in the D2D grant orDCI format 3/3A. Regarding the TPC command range indicated in the D2Dgrant or DCI format 3/3A, it could be only zero/negative value, forexample, {0, −10}dB.

The benefits of the above embodiment are: the eNB could relativelyaccurately control the D2D power to LTE WAN interference as it mimicsthe power of PUSCH for the D2D communication; it does not needindependent power accumulation specially for the D2D; the LTE WAN poweraccumulation is not impacted by the D2D communication; and the receivedpower in the eNB side is relatively stable (friendly to AGC).

According to another embodiment, if the uplink channel is a PUCCH or anSRS, the PUCCH or SRS's power value is considered as the reference forthe D2D power control. In this case, for example, the formula (3) isused for computing the power value of the D2D user equipment:

10 log₁₀(M _(D2D,c)(i))+P _(D2D,c)(j)+α_(D2D,c)(j)·PL_(c)+Δ_(TF,c)(i)+0.5(f _(c)(i−1)+g(i−1))+δ_(D2D,c)(i−K _(D2D))   (3)

Here, the parameter “g(i−1)” is the latest PUCCH power controladjustment state.

According to another embodiment of the present disclosure, in the abovepower control method, the DCI format 3/3A could combine a TPC command ofthe LTE WAN communication and a TPC command of the D2D communication orjust consist of the TPC commands of the D2D communication.

FIG. 4 shows an example of multiple D2D groups in the same serving cellaccording to an embodiment of the present disclosure.

As shown in FIG. 4 , for example, there are multiple D2D groups (onlytwo groups are shown herein, but it is not limited to two groups) in thesame cell. Then, the eNB will indicate several sets of power controlparameters via an SIB, for example, the first set of {P₀, alpha} isindicated for the D2D group 1, and the second set of {P₀, alpha} isindicated for the D2D group 2. That is, according to an embodiment ofthe present disclosure, in the above power control method, the P₀ andalpha are configured differently among D2D user equipment groups in thesame cell via an SIB.

According to another embodiment of the present disclosure, differentpower control parameters, such as P₀ and alpha of D2D communication, aredifferentiated based on the resource allocation mode of the D2D or RRCstatus. For example, P₀ and alpha of D2D communication are configuredseparately for mode 1 and mode 2 from D2D resource allocation point ofview. Or for example, P₀ and alpha of D2D communication are configuredseparately for user equipments in RRC_CONNECTED and user equipments inRRC_IDLE. Furthermore, for a user equipment in the RRC_CONNECTED status,P₀ and alpha of D2D communication are configured by dedicated RRCsignaling.

According to an embodiment of the present disclosure, in the above powercontrol method, when the uplink channel is a PUSCH, the P_(D2D,c)(j) maybe configured differently from P_(O_PUSCH,c)(j), and the α_(D2D,c)(j)may be configured differently from α_(c)(j), in the power control ofuplink channel of the same user equipment in the LTE wide area network,and they are signaled by RRC or MAC signaling.

FIG. 5 shows a block diagram of the user equipment according to anembodiment of the present disclosure.

As shown in FIG. 5 , the user equipment 500 used in the device to device(D2D) communication according to an embodiment of the present disclosureincludes a computing unit 501. The computing unit 501 is configured tocompute a power value of device to device (D2D) transmission of a userequipment performing D2D communication in a subframe in a serving cell,based on a power control adjustment state of an LTE wide area network(WAN) uplink channel of the user equipment and an offset or a ratioindicated by a TPC command indicated in D2D grant or DCI format 3/3A.

According to another embodiment of the present disclosure, in the userequipment 500, the uplink channel is any of a PUSCH, an SRS, and a PUCCHor a combination of them.

According to another embodiment of the present disclosure, in the userequipment 500, the power value is further decided by open-loopparameters including P₀ and alpha of D2D communication configured by MAClayer signaling or RRC signaling.

According to another embodiment of the present disclosure, in the userequipment 500, the offset and ratio indicate only zero or a negativevalue.

According to another embodiment of the present disclosure, in the userequipment 500, the DCI format 3/3A could combine a TPC command of LTEWAN communication and a TPC command of D2D communication or just consistof the TPC commands of D2D communication.

According to another embodiment of the present disclosure, in the userequipment 500, the P₀ and alpha of D2D communication are configuredseparately for a user equipment in an RRC_CONNECTED status and a userequipment in an RRC_IDLE status.

According to another embodiment of the present disclosure, in the userequipment 500, the P₀ and alpha of D2D communication are configuredseparately based on a resource allocation mode which could be mode 1 inwhich the eNB or release-10 relay node schedules exact resources used bythe user equipment or mode 2 in which the user equipment on its ownselects resources from resource pools.

According to another embodiment of the present disclosure, in the userequipment 500, for a user equipment in an RRC_CONNECTED status, the P₀and alpha of D2D communication are configured by dedicated RRCsignaling.

According to another embodiment of the present disclosure, in the userequipment 500, P₀ and alpha are configured differently among D2D userequipment groups in the same cell via an SIB.

According to another embodiment of the present disclosure, the userequipment 500 may further include a central processing unit (CPU) 502for executing related programs to process various kinds of data andcontrol the operations of respective units in the user equipment 500; aread-only memory (ROM) 503 for storing various programs required by theCPU to perform various kinds of processing and controls; a random accessmemory (RAM) 504 for storing intermediate data temporarily generated bythe CPU in the processing and control procedure; an input/output (I/O)unit 505 for connecting to the outside devices to transmit various kindsof data between an outside device and the user equipment 500 accordingto an embodiment of the present disclosure; and a user interface (I/F)unit 506 which includes a keyboard, a mouse, a touch pad, and otherdevices implemented by various devices that may interact with the user.These devices or units may be coupled to the computing unit 501 and soon in the user equipment 500 via a bus to perform various controls andrelated operations to realize various corresponding functions of thepresent disclosure.

According to an embodiment of the present disclosure, the functions ofthe computing unit 501 may be realized by storing a program in the ROM503 and executing the program in the CPU 502. According to an embodimentof the present disclosure, respective devices (units) in the userequipment 500 may be implemented by combining into one unit. Theirspecific implementation does not limit the scope of the presentdisclosure.

Based on the above description, the present disclosure proposes to mimicLTE WAN's power of the same user equipment for D2D transmission in orderto make the LTE WAN interference controllable, for example, the PUSCHadjustment state (e.g., fco) is used as reference for D2D accumulationpower. In this case, there is no need for special accumulationimplementation for D2D user equipment within D2D subframes. Theopen-loop parameters like alpha and P₀ in D2D communication could be setin the same manner as those in LTE WAN communication. The offset orratio to the PUSCH adjustment state (for example fco), which would beindicated in a TPC command in D2D grant or DCI format 3/3A, is used tofurther adjust the D2D power to LTE WAN interference. In variantsolutions, any other LTE WAN channel's power or a combination of them ofthe same user equipment could be referred for the D2D power. And in theproposals, open-loop parameters like P₀ and alpha of D2D communicationcould be configured differently between mode 1 and mode 2, or betweenRRC_IDLE and RRC_CONNECTED statuses. And open-loop parameters like P₀and alpha used by D2D communication could be indicated by dedicated RRCparameters. And the SIB could indicate several sets of open-loopparameters to support multiple D2D groups in the same cell; for example,a first set of {P₀, alpha} is used for D2D group 1, and a second set of{P₀, alpha} is used for D2D group 2.

The present disclosure can be realized by software, hardware, orsoftware in cooperation with hardware. Each functional block used in thedescription of the embodiments described above can be realized by an LSIas an integrated circuit. They may be individually formed as chips, orone chip may be formed so as to include a part or all of the functionalblocks. The LSI here may be referred to as an IC, a system LSI, a superLSI, or an ultra LSI depending on a difference in the degree ofintegration. However, the technique of implementing an integratedcircuit is not limited to the LSI and may be realized by using adedicated circuit or a general-purpose processor. In addition, a fieldprogrammable gate array (FPGA) that can be programmed after themanufacture of the LSI or a reconfigurable processor in which theconnections and the settings of circuits cells disposed inside the LSIcan be reconfigured may be used. Further, the calculation of eachfunctional block can be performed by using a calculating device, forexample, including a DSP or a CPU, and the processing step of eachfunction may be recorded on a recording medium as a program forexecution. Furthermore, when a technology for implementing an integratedcircuit that substitutes the LSI appears in accordance with theadvancement of the semiconductor technology or other derivativetechnologies, it is apparent that the functional block may be integratedby using such technologies.

It is noted that the present disclosure intends to be variously changedor modified by those skilled in the art based on the descriptionpresented in the specification and known technologies without departingfrom the content and the scope of the present disclosure, and suchchanges and applications fall within the scope that is claimed to beprotected. Furthermore, in a range not departing from the content of thedisclosure, the constituent elements of the above-described embodimentsmay be arbitrarily combined.

1. An integrated circuit, comprising: configuration circuitry, which, inoperation, controls configuring a first set of parameters and a secondset of parameters for device to device (D2D) communicationindependently; and transmission circuitry, which, in operation, controlstransmitting to a communication apparatus of the D2D communication thefirst set of parameters and the second set of parameters, wherein atransmission power for the D2D communication is determined using aTransmit Power Command (TPC) included in a D2D grant withoutaccumulating one or more previous TPCs, and using one of: the first setof parameters for D2D transmission mode 1 or the second set ofparameters for D2D transmission mode 2, and wherein the transmissionpower for the D2D communication is determined using a pathloss (PL)value that is a downlink path loss estimate value for a serving cell. 2.The integrated circuit according to claim 1, wherein the D2Dtransmission mode 1 is a transmission mode where a scheduling of the D2Dcommunication is performed by a base station, and the D2D transmissionmode 2 is another transmission mode where a scheduling of the D2Dcommunication is performed by the communication apparatus.
 3. Theintegrated circuit according to claim 1, wherein the D2D transmissionmode 1 is for an RRC_CONNECTED user equipment and the D2D transmissionmode 2 is for at least an RRC_IDLE user equipment.
 4. The integratedcircuit according to claim 1, wherein the first set of parameters andthe second set of parameters are transmitted via a Radio ResourceControl (RRC) signaling.
 5. The integrated circuit according to claim 1,wherein the first set of parameters includes a first P₀ and a first afor the D2D transmission mode 1 and the second set of parametersincludes a second P₀ and a second a for the D2D transmission mode 2,wherein the first P₀ and the second P₀ are each a power parameter andthe first a and the second a are each a pathloss-related coefficient. 6.The integrated circuit according to claim 1, wherein the first set ofparameters is configured for a first group of user equipments and thesecond set of parameters is configured for a second group of userequipments that is different from the first group of user equipments. 7.The integrated circuit according to claim 1, wherein a transmissionpower for another communication between the communication apparatus anda base station is determined using the TPC included in a grant for theother communication with accumulating one or more previous TPCs includedin grants of the other communication.
 8. The integrated circuitaccording to claim 1, wherein the first set of parameters is differentfrom the second set of parameters.